This invention relates generally to an aluminum base alloy bearing having an intermediate bonding layer formed between a back metal layer and an aluminum base bearing alloy layer, and more particularly to an aluminum base alloy bearing of the type in which a fatigue resistance is improved, directing attention to the hardness and thickness of an intermediate bonding layer.
There is well known an aluminum base alloy bearing which has an intermediate bonding layer formed between a back metal layer and an aluminum base bearing alloy layer for the purpose of increasing the strength of bonding between them.
An aluminum base alloy bearing is relatively excellent in fatigue resistance, and has a high strength, and therefore has been used as a bearing for a shaft repeatedly subjected to high loads, such as a crankshaft of an engine of an automobile or an ordinary industrial machine. With a high output design of the engine, the aluminum base alloy bearing has now been required to have a higher fatigue resistance.
Under the circumstances, there have been proposed aluminum base alloy bearings in which attention is directed to an intermediate bonding layer, and the intermediate bonding layer is improved to thereby enhance a fatigue resistance. Such aluminum base alloy bearings are disclosed in JP-B2-5-53966 and JP-A-3-168411.
In the aluminum base alloy bearing disclosed in the above JP-B2-5-53966, the hardness of the intermediate bonding layer is decreased to directly enhance conformability, and a fatigue resistance is enhanced indirectly through the enhanced conformability. More specifically, if a shaft is inclined due to manufacturing errors of the shaft, a bearing and a housing, an uneven contact develops between the shaft and a bearing alloy layer because of this inclination, so that a large concentrated load acts on this uneven contact portion, thereby lowering the fatigue resistance. In order to overcome this difficulty, the hardness of the intermediate bonding layer is decreased so that this intermediate bonding layer can function as a cushioning material for the bearing alloy layer. By doing so, the conformability of the bearing alloy layer is enhanced, thereby alleviating the uneven contact between the shaft and the bearing alloy.
In the aluminum base alloy bearing disclosed in the above JP-A-3-168411, the hardness of the intermediate bonding layer is increased to a level not exceeding that of a bearing alloy layer, so that the intermediate bonding layer reinforces the bearing alloy layer while not affecting the cushioning property and hence conformability of the intermediate bonding layer as much as possible, thereby enhancing the fatigue resistance.
However, the inventors of the present invention have found that the fatigue resistance of the bearing is insufficient in spite of the endeavor explained above.